A new, original, ornamental design for a kettle, as shown and described.
FIG. 1 is a front view of a kettle showing my new design;
FIG. 2 is a left view thereof;
FIG. 3 is a right view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a perspective view thereof; and,
FIG. 7 is another perspective view thereof.
A back view is completely mirrored with the front view, which is thus omitted in the drawings. The broken lines in the drawing depict environmental subject matter only and form no part of the claimed design.